Betulin-containing birch bark extracts and their formulation

ABSTRACT

The present disclosure relates to birch bark extracts, methods of producing such extracts, stable pharmaceutical compositions containing such extracts and methods of using of such extracts. The birch bark extracts of the present disclosure contain triterpenes, which are known to improve wound healing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/120,678, filed Dec. 14, 2020, which is a continuation of U.S.application Ser. No. 16/959,098, filed Jun. 29, 2020, which is a U.S.National Stage Application under 35 U.S.C. § 371 of InternationalApplication No. PCT/EP2019/050186, filed Jan. 4, 2019, which claims thebenefit of priority to U.S. Provisional Application No. 62/613,646,filed Jan. 4, 2018, the entire contents of which are hereby incorporatedby reference in their entireties for all purposes.

FIELD OF THE DISCLOSURE

The present disclosure relates to pharmaceutical formulations derivedfrom the extracts of birch bark.

BACKGROUND OF THE DISCLOSURE

The triterpenes found in birch bark extracts are known to have woundhealing properties. Methods of extracting these triterpenes from birchbark are reported in U.S. Pat. No. 7,482,383. These methods providesolid birch bark extracts that may be used in pharmaceuticalformulations. For example, emulsions containing such extracts aredescribed in U.S. Pat. No. 7,482,383, and oleogels containing suchextracts are described in U.S. Pat. Nos. 9,352,041; 8,828,444 and8,536,380.

For clinical use in wound healing, an oleogel must be applied by touchto the area of the skin where treatment is needed. Touch application isdisadvantageous for the treatment of certain skins conditions (e.g.,epidermolysis bullosa) because the simple act of applying the oleogelmay lead to worsening of the skin condition.

Therefore, there is a need for wound-healing formulations containingsolid birch bark extracts that may be applied to the skin withoutworsening the patient's condition.

The present disclosure provides clinically-advantageous wound-healingformulations (including oleogels, emulsions and foams) with improvedrheological properties which overcome the disadvantages of the knownsolid birch bark-containing emulsions and oleogels.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a solid birch bark extract that containsat least about 70% by weight of betulin and one or more triterpenesselected from the group consisting of betulinic acid, oleanolic acid,erythrodiol and lupeol. The solid birch bark extracts described hereinmay be formulated in an oleogel that possesses clinically-advantageousrheological properties.

The present disclosure also provides a method of making a solid birchbark extract that may be dispersed in a nonpolar solvent to provide aclinically-advantageous oleogel comprising the steps of (a) contactingbirch bark with a suitable solvent to form an extraction solutioncontaining betulin and at least one triterpene; (b) separating the birchbark from the extraction solution; (c) cooling the extraction solutionto crystallize a portion of the betulin and triterpene from thesolution; (d) separating the crystallized betulin and triterpene; (e)drying the separated, crystallized betulin and triterpene to form asolid birch bark extract. The present disclosure also provides the solidbirch bark extracts that are prepared according to these methods.

The present disclosure provides a clinically-advantageous oleogelcomprising about 1% to about 20% by weight of particles of the solidbirch bark extract dispersed in about 80% to about 99% of one or morenonpolar liquids the solid birch bark extracts are dispersed in asuitable nonpolar liquid to form an oleogel. A sterile wound dressingcomprising a pad and a therapeutically effective amount of the oleogelis also provided.

The present disclosure provides an emulsion comprising an oleogel of thepresent invention and further provides a foam comprising an emulsion ofthe present disclosure.

The present disclosure also provides methods of treating a wound in apatient by topically administering an effective amount of an oleogel, anemulsion or a foam of the present disclosure to at least a portion ofthe wound.

The present disclosure also provides methods of treating epidermolysisbullosa in a patient in need thereof comprising topically administeringan effective amount of an oleogel, an emulsion or a foam of the presentdisclosure to an area of epidermolysis bullosa of the patient.

The present disclosure provides a solid birch bark extract, oleogel,sterile wound dressing, process of preparation, emulsion, foam,pressurized container, method of treating a wound, and method oftreating epidermolysis bullosa according to the following numberedembodiments:

-   1. A solid birch bark extract comprising at least about 70 wt. %    betulin and one or more triterpenes selected from the group    consisting of betulinic acid, oleanolic acid, erythrodiol, and    lupeol.-   2. The sold birch bark extract of embodiment 1, wherein the solid    birch extract has an HPLC chromatogram substantially identical to    FIG. 1 when chromatographed according to the following HPLC method:

Time H₃PO₄ Flow rate (min) Acetonitrile Water (v/v) (ml/min) 0 30 700.1% 0.6 5 30 30 0.1% 0.6 15 98 2 0.1% 0.6 20 98 2 0.1% 0.6 21 30 700.1% 0.6 30 30 70 0.1% 0.6

-   -   Column: C18, 2.6 μm, 150×2.1 mm; detector: 210 and 320 nm;

-   wherein the betulinic acid has a relative retention time of about    0.75-0.90, the oleanolic acid has a relative retention time of about    0.84-0.97, the betulin has a relative retention time of 1.00, the    erythrodiol has a relative retention time of about 1.25-1.40, and    the lupeol has a relative retention time of about 3.50-4.15.

-   3. The solid birch bark extract of embodiment 1 or 2, prepared by a    process comprising:    -   (a) contacting birch bark with a pharmaceutically acceptable        solvent, thereby forming an extraction solution comprising        betulin and one or more triterpenes;    -   (b) separating the birch bark from the extraction solution;    -   (c) cooling the extraction solution whereby a portion of the        betulin and one or more triterpenes crystallizes from the cooled        extraction solution;    -   (d) separating the crystallized betulin and one or more        triterpenes from the cooled extraction solution;    -   (e) drying the separated, crystallized betulin and one or more        triterpenes to provide the solid birch bark extract;    -   wherein if after drying, about 1 wt. % to about 20 wt. % of the        dried solid birch bark extract of step (e) dispersed in refined        sunflower oil forms an oleogel.

-   4. The solid birch bark extract of embodiment 3, wherein one or more    of steps (a), (c), and (e) is carried out under the following    conditions:    -   (i) said contacting of step (a) is carried out at a temperature        of about 60° C. to about 130° C.;    -   (ii) said cooling of step (c) is carried out at a temperature of        about −20° C. to about 35° C.;    -   (iii) said drying of step (e) is carried out at a temperature of        about 75° C. to about 95° C. at a pressure of less than about 70        mbar.

-   5. The solid birch bark extract of embodiment 3, wherein two or more    of steps (a), (c), and (e) are carried out under the following    conditions:    -   (i) said contacting of step (a) is carried out at a temperature        of about 60° C. to about 130° C.;    -   (ii) said cooling of step (c) is carried out at a temperature of        about −20° C. to about 35° C.;    -   (iii) said drying of step (e) is carried out at a temperature of        about 75° C. to about 95° C. at a pressure of less than about 70        mbar.

-   6. The solid birch bark extract of embodiment 3, wherein steps (a),    (c), and (e) are carried out under the following conditions:    -   (i) said contacting of step (a) is carried out at a temperature        of about 60° C. to about 130° C.;    -   (ii) said cooling of step (c) is carried out at a temperature of        about −20° C. to about 35° C.;    -   (iii) said drying of step (e) is carried out at a temperature of        about 75° C. to about 95° C. at a pressure of less than about 70        mbar.

-   7. The solid birch bark extract of any one of embodiments 3-6,    wherein the pharmaceutically acceptable solvent is a hydrocarbon or    alcohol, or combinations thereof

-   8. The solid birch bark extract of any one of embodiments 3-7,    wherein the pharmaceutically acceptable solvent is a hydrocarbon    selected from the group consisting of n-pentane, n-hexane, or    n-heptane.

-   9. The solid birch bark extract of embodiment 8, wherein the    pharmaceutically acceptable solvent is n-heptane, and said    contacting is carried out at a temperature of about 60° C. to about    130° C. for about 8-12 minutes.

-   10. The solid birch bark extract of any one of embodiments 3-9,    wherein in step (c) the cooled extraction solution is supersaturated    at least about 2-fold.

-   11. The solid birch bark extract of embodiment 10, wherein the    cooled extraction solution is supersaturated about 5-fold.

-   12. The solid birch bark extract of any of embodiments 3-11, wherein    the amount of residual extraction solvent is no more than about 0.5    wt. %.

-   13. An oleogel comprising about 1 wt. % to about 20 wt. % of    particles of the solid birch bark extract of any one of embodiments    1-12, having an average particle size of less than about 50 μm,    dispersed in about 80 wt. % to about 99 wt. % of one or more    nonpolar liquids.

-   14. The oleogel of embodiment 13, wherein the dispersed solid birch    bark extract particles are the only oleogel forming agent in the    oleogel.

-   15. The oleogel of embodiment 13 or 14, comprising about 10 wt. % of    particles of the solid birch bark extract.

-   16. The oleogel of any one of embodiments 13 to 15, wherein the    nonpolar liquid comprises at least one triglyceride.

-   17. The oleogel of any one of embodiments 13 to 16, wherein the    nonpolar liquid comprises at least one C7 or greater hydrocarbon.

-   18. The oleogel of embodiment 16, wherein the nonpolar liquid    comprises one or more vegetable oils.

-   19. The oleogel of embodiment 18, wherein the nonpolar liquid    comprises sunflower oil.

-   20. The oleogel of any one of embodiments 13-19, wherein the    nonpolar liquid has a peroxide value less than about 10.

-   21. The oleogel of embodiment 20, wherein the peroxide value is no    more than about 3.

-   22. The oleogel of any one of embodiments 13-21, wherein the oleogel    is substantially free of solid birch bark extract particles having a    size greater than about 50 μm.

-   23. The oleogel of any one of embodiments 13-22, wherein the oleogel    is sterile.

-   24. The oleogel of embodiment 23, wherein the oleogel is sterilized    by ionizing irradiation at doses less than about 20 kGy.

-   25. The oleogel of embodiment 24, wherein the oleogel is sterilized    by ionizing irradiation at doses ranging from about 11 to about 20    kGy.

-   26. The oleogel of any one of embodiments 13-25, wherein the    segregation of the nonpolar liquid from the oleogel is less than    about 10% after centrifuging at 25° C. for 30 min at 2750 g.

-   27. The oleogel of any one of embodiments 13-26, wherein the    viscosity at 200/s of the oleogel ranges from about 0.5 to about 4.0    Pa·s and the thixotropy value of the oleogel ranges from about 200    to about 1200 Pa·s as measured according to the rotating viscometer    method described in Ph. Eur. 2.2.10 using a cone-plate viscometer.

-   28. The oleogel of any one of embodiments 13-27, wherein the    consistency of the oleogel ranges from about 300-3000 mN as measured    according using a texture analyser.

-   29. The oleogel of any one of embodiments 13-28, further comprising    a disinfectant.

-   30. The oleogel of embodiment 29, wherein the disinfectant is    selected from the group consisting of ethanol, n-propanol, and    isopropanol.

-   31. The oleogel of any one of embodiments 13-28, further comprising    a lipophilic antibiotic.

-   32. A sterile wound dressing comprising:    -   (a) a pad, and    -   (b) a therapeutically effective layer comprising the oleogel of        any of embodiments 13-31 disposed on at least one surface of the        pad.

-   33. The sterile wound dressing of embodiment 32, wherein the pad is    an absorbent pad.

-   34. A process for preparing the solid birch bark extract of    embodiment 1 or 2, comprising:    -   (a) contacting birch bark with a pharmaceutically acceptable        solvent, thereby forming an extraction solution comprising        betulin and one or more triterpenes;    -   (b) separating the birch bark from the extraction solution;    -   (c) cooling the extraction solution whereby a portion of the        betulin and one or more triterpenes crystallizes from the cooled        extraction solution;    -   (d) separating the crystallized betulin and one or more        triterpenes from the cooled extraction solution;    -   (e) drying the separated, crystallized betulin and one or more        triterpenes to provide the solid birch bark extract;    -   wherein after drying, about 1 wt. % to about 20 wt. % of the        dried solid birch bark extract of step (e) dispersed in refined        sunflower oil forms an oleogel.

-   35. The process of embodiment 34, wherein one or more of steps (a),    (c), and (e) is carried out under the following conditions:    -   (i) said contacting of step (a) is carried out at a temperature        of about 60° C. to about 130° C.;    -   (ii) said cooling of step (c) is carried out at a temperature of        about −20° C. to about 35° C.;    -   (iii) said drying of step (e) is carried out at a temperature of        about 75° C. to about 95° C. at a pressure of less than about 70        mbar.

-   36. The process of embodiment 34, wherein two or more of steps (a),    (c), and (e) are carried out under the following conditions:    -   (i) said contacting of step (a) is carried out at a temperature        of about 60° C. to about 130° C.;    -   (ii) said cooling of step (c) is carried out at a temperature of        about −20° C. to about 35° C.;    -   (iii) said drying of step (e) is carried out at a temperature of        about 75° C. to about 95° C. at a pressure of less than about 70        mbar.

-   37. The process of embodiment 34, wherein steps (a), (c), and (e)    are carried out under the following conditions:    -   (i) said contacting of step (a) is carried out at a temperature        of about 60° C. to about 130° C.;    -   (ii) said cooling of step (c) is carried out at a temperature of        about −20° C. to about 35° C.;    -   (iii) said drying of step (e) is carried out at a temperature of        about 75° C. to about 95° C. at a pressure of less than about 70        mbar.

-   38. The process of any one of embodiments 34-37, wherein the    pharmaceutically acceptable solvent is a hydrocarbon selected from    the group consisting of n-pentane, n-hexane, or n-heptane.

-   39. The process of any one of embodiments 34-38, wherein the    pharmaceutically acceptable solvent is n-heptane, and said    contacting is carried out at a temperature of about 115° C. to about    130° C. for about 8-12 minutes.

-   40. The process of any one of embodiments 34-39, wherein in step (c)    the cooled extraction solution is supersaturated at least about    2-fold.

-   41. The process of embodiment 40, wherein the cooled extraction    solution is supersaturated about 5-fold.

-   42. The process of any of embodiments 34-41, wherein the amount of    residual extraction solvent is no more than about 0.5 wt. %.

-   43. An emulsion comprising the solid birch bark extract of any of    embodiments 1-12.

-   44. An emulsion comprising the oleogel of any of embodiments 13-31.

-   45. The emulsion of embodiment 43 or 44, wherein said emulsion is a    water-in-oil emulsion.

-   46. The emulsion of embodiment 45, substantially free of emulsifier.

-   47. The emulsion of any one of embodiments 43-46, consisting    essentially of the solid birch bark extract or oleogel, oil, and    water.

-   48. The emulsion of any one of embodiments 44-46, consisting of the    oleogel, oil and water.

-   49. The emulsion of any one of embodiments 43-46, further comprising    a disinfectant.

-   50. The emulsion of embodiment 49, wherein the disinfectant is    selected from the group consisting of ethanol, n-propanol, and    isopropanol.

-   51. The emulsion of any one of embodiments 43-46, further comprising    a lipophilic antibiotic.

-   52. A foam comprising the emulsion of any one of embodiments 43-51.

-   53. The foam of embodiment 52, further comprising a disinfectant.

-   54. The foam of embodiment 53, wherein the disinfectant is selected    from the group consisting of ethanol, n-propanol, and isopropanol.

-   55. The foam of embodiment 52, further comprising a lipophilic    antibiotic.

-   56. The foam of any of embodiments 52-55, wherein the interfacial    surface tension of the emulsion is greater than about 4 mN/m.

-   57. The foam of any of embodiments 52-56, wherein the foam index is    greater than about 2.

-   58. The foam of embodiment 52, wherein the oleogel consists of about    5 wt. % to about 10 wt. % solid birch bark extract and the emulsion    is a water-in-oil emulsion consisting of the oleogel and about 20    wt. % to about 30 wt. % of water.

-   59. The foam of embodiment 58, wherein the oleogel consists of about    7 wt. % solid birch bark extract and the amount of water in the    emulsion is about 25 wt. %.

-   60. The foam of any of embodiments 52-56, further comprising an    emulsifier selected from the group consisting of phosphatidyl    choline, polyglyceryl-3-methyl glucose distearate, and combinations    thereof

-   61. A pressurized container filled with a mixture comprising the    emulsion of any one of embodiments 43-51 and a pharmaceutically    acceptable propellant, whereby the emulsion forms a foam upon    decanting at least a portion of the mixture from the container.

-   62. A method of treating a wound in a patient comprising topically    administering the oleogel of any one of embodiments 13-31 to at    least a portion of the wound.

-   63. The oleogel of any one of embodiments 13-31, for use in a method    of treating a wound.

-   64. The method or oleogel for use of embodiment 63, wherein the    wound is selected from the group consisting of a burns, surgical    skin lesions, superficial injuries, chronic wounds, pressure ulcers,    diabetic foot ulcers, chronic venous ulcers, artery insufficiency    ulcers, wounds from aesthetic skin treatments, wounds from ablative    laser skin treatments, wounds from chemical peels, wounds from    dermabrasion, wounds resulting from adverse drug reactions, wounds    resulting from toxic epidermal necrolysis, wounds resulting from    Lyell syndrome, wounds resulting from Stevens-Johnson syndrome, and    wounds resulting from radiation dermatitis.

-   65. A method of treating a wound in a patient comprising topically    administering the emulsion of any one of embodiments 43-51 to at    least a portion of the wound.

-   66. The emulsion of any one of embodiments 43-51, for use in a    method of treating a wound.

-   67. The method or emulsion for use of embodiment 66, wherein the    wound is selected from the group consisting of burns, surgical skin    lesions, superficial injuries, chronic wounds, pressure ulcers,    diabetic foot ulcers, chronic venous ulcers, artery insufficiency    ulcers, wounds from aesthetic skin treatments, wounds from ablative    laser skin treatments, wounds from chemical peels, wounds from    dermabrasion, wounds resulting from adverse drug reactions, wounds    resulting from toxic epidermal necrolysis, wounds resulting from    Lyell syndrome, wounds resulting from Stevens-Johnson syndrome, and    wounds resulting from radiation dermatitis.

-   68. A method of treating a wound in a patient comprising topically    administering the foam of any one of embodiments 52-60 to at least a    portion of the wound.

-   69. The foam of any one of embodiments 52-60, for use in a method of    treating a wound.

-   70. The method or foam for use of embodiment 69, wherein the wound    is selected from the group consisting of burns, surgical skin    lesions, superficial injuries, chronic wounds, pressure ulcers,    diabetic foot ulcers, chronic venous ulcers, artery insufficiency    ulcers, wounds from aesthetic skin treatments, wounds from ablative    laser skin treatments, wounds from chemical peels, wounds from    dermabrasion, wounds resulting from adverse drug reactions, wounds    resulting from toxic epidermal necrolysis, wounds resulting from    Lyell syndrome, wounds resulting from Stevens-Johnson syndrome, and    wounds resulting from radiation dermatitis.

-   71. A method of treating epidermolysis bullosa in a patient in need    thereof comprising topically administering to an area of    epidermolysis bullosa of the patient the oleogel of any one of    embodiments 13-31.

-   72. The oleogel of any one of embodiments 13-31, for use in a method    of treating epidermolysis bullosa.

-   73. A method of treating epidermolysis bullosa in a patient in need    thereof comprising topically administering to an area of    epidermolysis bullosa of the patient the emulsion of any one of    embodiments 43-51.

-   74. The emulsion of any one of embodiments 43-51, for use in a    method of treating epidermolysis bullosa.

-   75. A method of treating epidermolysis bullosa in a patient in need    thereof comprising topically administering to an area of    epidermolysis bullosa of the patient the foam of any one of    embodiments 52-60.

-   76. The foam of any one of embodiments 52-60, for use in a method of    treating epidermolysis bullosa.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1. shows the HPLC chromatograph taken from a solid birch barkextract monitoring 210 nm (top figure) and 320 nm (bottom figure). Thex-axis in FIG. 1 is the retention time (min), and the y-axis is the peakintensity (mAU).

FIG. 2. illustrates the continuous extraction of birch bark to providean extraction solution comprising betulin and one or more triterpenes.

DETAILED DESCRIPTION OF THE DISCLOSURE Definitions

While the following terms are believed to be well understood by one ofordinary skill in the art, the following definitions are set forth tofacilitate explanation of the presently disclosed subject matter.

It is to be understood that the terminology used herein is for thepurpose of describing particular embodiments only and is not intended tobe limiting.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of ordinary skillin the art to which this disclosure belongs. Preferred methods, devices,and materials are described, although any methods and materials similaror equivalent to those described herein can be used in the practice ortesting of the present disclosure. All references cited herein(including U.S. Pat. Nos. 9,352,041; 8,828,444; 8,536,380; and7,482,383) are incorporated for all purposes by reference in theirentirety.

Following long-standing patent law convention, the terms “a”, “an”, and“the” refer to “one or more” when used in this application, includingthe claims. Thus, for example, reference to “a carrier” includesmixtures of one or more carriers, two or more carriers, and the like.

Unless otherwise indicated, all numbers expressing quantities ofingredients, reaction conditions, and so forth used in the specificationand claims are to be understood as being modified in all instances bythe term “about”. Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the present specification and attachedclaims are approximations that can vary depending upon the desiredproperties sought to be obtained by the present application. Generallythe term “about”, as used herein when referring to a measurable valuesuch as an amount of weight, time, dose, etc. is meant to encompass inone example variations of ±15% or ±10%, in another example±5%, inanother example±1%, and in yet another example±0.1% from the specifiedamount, as such variations are appropriate to perform the disclosedmethod.

“Administering” includes any mode of administration, such as oral,subcutaneous, sublingual, transmucosal, parenteral, intravenous,intra-arterial, buccal, sublingual, topical, vaginal, rectal,ophthalmic, otic, nasal, inhaled, and transdermal. “Administering” canalso include prescribing or filling a prescription for a dosage formcomprising a particular compound. “Administering” can also includeproviding directions to carry out a method involving a particularcompound or a dosage form comprising the compound.

As used herein, the verb “comprise” as is used in this description andin the claims and its conjugations are used in its non-limiting sense tomean that items following the word are included, but items notspecifically mentioned are not excluded.

The term “birch bark” means the cortex of white-barked birch trees.Preferred embodiments include birch bark derived from Betula pendulaRoth and Betula pubescens Ehrh as well as hybrids of both species.

The term “relative retention time” (or “RRT”) means ratio of theretention time of the unknown peak to the retention time the betulinpeak and is calculated according to the following equation:RRT=RT_(unknown)/RT_(betulin)

-   -   where RT_(unknown) is the retention time of the unknown peak and        RT_(betulin) is the retention time of betulin peak (210 nm)        measured by the following HPLC method:

Time H₃PO₄ Flow rate (min) Acetonitrile Water (v/v) (ml/min) 0 30 700.1% 0.6 5 30 30 0.1% 0.6 15 98 2 0.1% 0.6 20 98 2 0.1% 0.6 21 30 700.1% 0.6 30 30 70 0.1% 0.6

-   -   Column: Phenomenex Kinetix C18, 2.6 μm, 150×2.1 mm.

The term “substantially identical” as used herein means an analyticalspectrum, such as HPLC chromatogram, NMR spectrum, and etc., whichresembles the reference spectrum to a great degree in both the peaklocations and their intensity. For example, a HPLC chromatogram is“substantially identical” to a reference chromatogram if the peaklocations (relative retention times) in the HPLC chromatogram vary by nomore than ±5% from the peak locations (relative retention times) in thereference chromatogram. In some embodiments, the relative peakintensities in the HPLC chromatogram may vary by no more than ±10% fromthe peak intensities in the reference chromatogram.

“Therapeutically effective amount” means the amount of an activesubstance that, when administered to a subject for treating a disease,disorder, or other undesirable medical condition, is sufficient to havea beneficial effect with respect to that disease, disorder, orcondition. The therapeutically effective amount will vary depending onthe chemical identity and formulation form of the active substance, thedisease or condition and its severity, and the age, weight, and otherrelevant characteristics of the patient to be treated. Determining thetherapeutically effective amount of a given active substance is withinthe ordinary skill of the art and typically requires no more thanroutine experimentation.

The term “substantially free” means that the ingredient indicated is notpresent, or is present in only insignificant amounts. In one embodiment,“substantially free” means less than about 10% (e.g. less than about 10wt. %). In other embodiments, “substantially free” means less than about5% (e.g. less than about 5 wt. %), less than about 2% (e.g. less thanabout 2 wt. %), or less than about 1% (e.g. less than about 1 wt. %), orabout 0% (e.g. about 0 wt. %). For example, an emulsion that issubstantially free of an emulsifier does not contain any emulsifier in asubstantial amount (e.g. contains less than about 10 wt. %, less thanabout 5 wt. %, less than about 2 wt. %, or less than about 1 wt. % of anemulsifier; or contains 0 wt. % of an emulsifier). Similarly, an oleogelthat is substantially free of solid birch bark extract particles havinga size greater than about 50 μm does not contain any solid birch barkextract particles having a size greater than about 50 μm in asubstantial amount (e.g. contains less than about 10 wt. %, less thanabout 5 wt. %, less than about 2 wt. %, or less than about 1 wt. % ofsolid birch bark extract particles having a size greater than about 50μm; or contains 0 wt. % of solid birch bark extract particles having asize greater than about 50 μm).

Solid Birch Bark Extracts

The present disclosure provides solid birch bark extracts that may beformulated in clinically-advantageous oleogels. Without being bound byany theory, it is believed that the chemical composition and theparticle morphology of the solid birch bark extracts produced accordingto the methods of the present disclosure are responsible theseadvantages.

The solid birch bark extracts of the present disclosure may becharacterized on the basis of their chemical composition. In someembodiments, the solid birch bark extracts of the present disclosurecomprise lupane and oleanane triterpenes. In particular, the birch barkextracts may contain the lupane triterpenes: betulin, lupeol, andbetulinic acid, and the oleanane triterpenes: erythrodiol and oleanolicacid.

The presence of a particular triterpene in the birch extract may bedetermined using relative retention times obtained from HPLCchromatography. The following HPLC method is used to determine thechemical composition of the solid birch bark extracts of the presentdisclosure:

Time H₃PO₄ Flow rate (min) Acetonitrile Water (v/v) (ml/min) 0 30 700.1% 0.6 5 30 30 0.1% 0.6 15 98 2 0.1% 0.6 20 98 2 0.1% 0.6 21 30 700.1% 0.6 30 30 70 0.1% 0.6

-   -   Column: Phenomenex Kinetix C18, 2.6 μm, 150×2.1 mm.

A Phenomenex Kinetix C18 column is exemplary of an HPLC column having aC-18 modified silica stationary phase on core-shell silica solid support(2.6 μm HILIC 100 Å) with the above noted column dimensions.

When a solid birch bark extract is subjected to the above-mentioned HPLCchromatography method betulinic acid has a relative retention time ofabout 0.75-0.90, oleanolic acid has a relative retention time of about0.84-0.97, betulin has a relative retention time of 1.00, erythrodiolhas a relative retention time of about 1.25-1.40, and lupeol has arelative retention time of about 3.50-4.15.

In certain embodiments, the solid birch bark extract has an HPLCchromatogram substantially identical to FIG. 1.

In some embodiments, the solid birch bark extract comprises at leastabout 50 wt. %, at least about 55 wt. %, at least about 60 wt. %, atleast about 65 wt. %, at least about 70 wt. %, at least about 75 wt. %,at least about 80 wt. %, at least about 85 wt. %, or at least about 90%by weight betulin and one or more triterpenes. In some embodiments, theone or more triterpenes is selected from the group consisting ofbetulinic acid, oleanolic acid, erythrodiol and lupeol.

In some embodiments, the solid birch bark extract comprises at least oneof the following substances: 3-β-caffeoyl betulin, acetate of themethylester of betulinic acid, acetyloleanolic acid, allobetulin,betulinic aldehyde, betulonic acid, betulonic aldehyde,lupane-3β,20,28-triol, lupane-3β,20-diol (monogynol), oleanolicaldehyde, sitosterol, ursolic acid, or β-amyrin

The solid birch bark extract of the present disclosure may becharacterized by the particle size of the particles of the solid birchbark extract. In some embodiments, the average particle size of theparticles of the solid birch bark extract is less than about 100 μm,less than about 90 μm, less than about 80 μm, less than about 70 μm,less than about 60 μm, less than about 50 μm, less than about 40 μm,less than about 30 μm or less than about 25 μm.

In other embodiments, the solid birch bark extract of the presentdisclosure is substantially free of solid birch bark extract particleshaving a particle size greater than about 30 μm, greater than about 40μm, greater than about 50 μm, greater than about 60 μm, greater thanabout 70 μm, greater than about 80 μm, greater than about 90 μm orgreater than about 100 μm.

In preferred embodiments, the solid birch bark extracts are derived fromBetula pendula Roth and Betula pubescens Ehrh as well as hybrids of bothspecies.

Solid Birch Bark Extract Manufacturing Processes

The present disclosure provides methods for preparing solid birch barkextracts that may be formulated in clinically-advantageous oleogels. Ingeneral, the methods include the steps of obtaining birch trees,stripping and processing the bark from said birch trees, contacting theprocessed birch bark with a suitable solvent to provide an extractionsolution comprising betulin and one or more triterpenes, and isolatingand drying the birch bark extract comprising betulin and one or moretriterpenes from the extraction solution. In some embodiments, theisolated the birch bark extract is in the form of a solid.

In some embodiments, the method comprises: (a) contacting birch barkwith a pharmaceutically acceptable solvent to form a extraction solutioncomprising betulin and one or more triterpenes; (b) separating the birchbark from the extraction solution; (c) cooling the extraction solutionwhereby a portion of the betulin and one or more triterpenescrystallizes from the cooled extraction solution; (d) separating thecrystallized betulin and one or more triterpenes from the cooledextraction solution; and (e) drying the separated, crystallized betulinand one or more triterpenes to provide the solid birch bark extract.

In some embodiments, the birch bark used in step (a) is first processedto improve the extraction efficiency of betulin and one or moretriterpenes from the birch bark. For example, experiments have shownthat the yield of the dry extract from birch bark is highest when theextracted birch bark particles are small. In certain embodiments, theparticle size of the birch bark is reduced prior to step (a) using amill, or other suitable equipment, until the resulting birch bark passesthrough a sieve with a mesh size of about 1.25 mm.

In some embodiments, the birch bark is contacted with a pharmaceuticallyacceptable solvent at a temperature of between about 50° C. and about200° C. In other embodiments, the temperature is between about 60° C.and about 100° C., between about 60° C. and about 110° C., between about60° C. to about 120° C., between about 60° C. to about 130° C., betweenabout 70° C. to about 130° C., between about 80° C. to about 130° C.,between about 90° C. to about 130° C., or between about 100° C. and 150°C. In certain further embodiments, the temperature is between about 115°C. and 130° C.

In some embodiments, the birch bark is contacted with a pharmaceuticallyacceptable solvent at a pressure between about 2 to 10 bars. In oneembodiment, the pressure is about 4.5 bars.

Pharmaceutically acceptable solvents are known to those of skill in theart and include hydrocarbons, alcohols, ketones, ethers esters,sulfoxides, etc. Examples of pharmaceutically acceptable solventsinclude, without limitation, 1-butanol, 1-pentanol, 1-propanol,2-butanol, 2-methyl-1-propanol, 2-propanol, 3-methyl-1-butanol, aceticacid, acetone, anisole, butyl acetate, dimethyl sulfoxide, ethanol,ethyl acetate, ethyl ether, ethyl formate, formic acid, heptane, hexane,isobutyl acetate, isopropyl acetate, methyl acetate, methylethyl ketone,methylisobutyl ketone, pentane, propyl acetate, tert-butylmethyl ether,diisopropyl ether, methyl tert-butyl ether, methylisopropyl ketone, andmethyltetrahydrofuran.

In some embodiments, two or more pharmaceutically acceptable solventsare mixed to provide the pharmaceutically acceptable solvent.

In some embodiments, the birch bark is contacted with n-heptane at atemperature of between about 60° C. and 130° C. for between 8 to 12minutes.

In some embodiments, the (a) contacting birch bark with apharmaceutically acceptable solvent to form an extraction solutioncomprising betulin and one or more triterpenes and (b) separating thebirch bark from the extraction solution are run using a continuousextraction process (Shown in FIG. 2).

In one embodiment of the continuous extraction process, birch bark ismixed with n-heptane in a proportion of about 1:14 to 1:16 (w/v). Themixture is extracted continuously using n-heptane as extraction solventat a temperature of about 115-130° C. and at a pressure of about 4.5 bar(Nitrogen). At the lower end of the sedimentation vessel the extractedcork is rinsed down by cold n-heptane, and at the upper end of thesedimentation vessel the extract (hot solution of triterpenes inn-heptane) is filtrated (10 μm filter) and transported through a secondfilter (1 μm filter) to the crystallisation step.

In some embodiments, the cooling of step (c) is carried out at atemperature of about −20° C. to about 35° C., about −15° C. to about 35°C., −10° C. to about 35° C., about −5° C. to about 35° C., or about 0°C. to about 35° C. In other embodiments, in step (c) the cooledextraction solution is supersaturated at least about 1-fold, about2-fold, about 3-fold, about 4-fold, about 5-fold or about 6-fold. Inpreferred embodiments, in step (c) the cooled extraction solution issupersaturated about 2-fold or about 5-fold.

In some embodiments, the drying step (e) is carried out under vacuum ata temperature of at least 50° C., at least 60° C., at least 70° C., atleast 80° C. or at least 85° C. In certain embodiments, the drying step(e) is carried out at a temperature of about 65° C. to about 75° C.,about 70° C. to about 80° C., about 75° C. to about 85° C., or about 85°C. to about 95° C.

In some embodiments, the drying step (e) is carried out under vacuum ata pressure of less than about 90 mbar, less than about 80 mbar, lessthan about 70 mbar, less than about 60 mbar or less than about 50 mbar.In certain embodiments, drying step (e) reduces the amount of thepharmaceutically acceptable solvent in the dry birch bark extract toless than about 0.5% (weight/weight).

The present invention also provides the solid birch bark extractsprepared according to the processes set forth above.

Compositions Comprising Solid Birch Bark Extracts

The present disclosure provides clinically-advantageous wound-healingformulations comprising solid birch bark extracts. The compositionsinclude oleogels, emulsions, foams, and oleogel-impregnated sterilewound dressings. The compositions are useful as topical wound healingagents.

Gels are finely dispersed systems comprising a liquid phase and a solidphase. The solid phase forms a coherent three-dimensional framework andthe two phases permeate one another. Oleogels are hydrophobic gels basedon a nonpolar liquid (for example, an oil, a wax, or a paraffin) towhich a gel-forming agent is added to achieve the desired physicalproperties.

The present disclosure provides oleogels comprising a nonpolar liquidand an oleogel-forming agent. Suitable nonpolar liquids for use inoleogels of the present disclosure include, for example, plant, animal,or synthetic oils, waxes, and paraffins. In some embodiments, thenonpolar liquid is a vegetable oil selected from the group consistingof: castor oil, peanut oil, jojoba oil, sunflower oil, olive oil,avocado oil, and almond oil. In a preferred embodiment, the nonpolarliquid is sunflower oil.

In some embodiments, the nonpolar liquid comprises at least onetriglyceride. In certain embodiments, the at least one triglyceride isMiglyol. In other embodiments, the nonpolar liquid comprises at leastone C7 or greater hydrocarbon. In certain embodiments, the at least oneC7 or greater hydrocarbon is a paraffin.

In some embodiments, the nonpolar liquid used in the oleogel has aperoxide value of least than about 15, less than about 10, less thanabout 5, less than about 4, less than about, 3 or less than about 2. Incertain embodiments, the nonpolar liquid has a peroxide value of no morethan about 3. The term “peroxide value” as used herein means theperoxide value is determined according to Ph. Eur. 2.5.5.

The present disclosure provides methods of making oleogels. In someembodiments, after the solid birch bark extract is dried, about 1 wt %to about 20 wt % of the dried solid birch bark extract is dispersed innonpolar liquid to form an oleogel. In certain embodiments, the nonpolarliquid is sunflower oil.

In certain embodiments, the oleogel is sterile. The oleogel may besterilized by suitable methods known to those skilled in the art, forexample using ionizing radiation such as electron beam (EB), X-ray, orgamma. In some embodiments, the oleogel is sterilized by ionizing (e.g.,gamma) irradiation at doses less than about 40 kGy, less than about 35kGy, less than about 30 kGy, less than about 25 kGy, less than about 20kGy, or less than about 15 kGY. In certain embodiments, the oleogel issterilized by ionizing (e.g., gamma) irradiation at doses ranging fromabout 5 to about 25 kGy, about 9 to about 25 kGy, about 10 to about 25kGy, about 11 to about 25 kGy, about 12 to about 25 kGy, or from about11 to about 20 kGy.

In some embodiments, the oleogel comprises between about 1 wt. % andabout 30 wt. % solid birch bark extract dispersed in about 70 wt. % toabout 99 wt. % of one or more nonpolar liquids, wherein the oleogelcontains at least one oleogel forming agent in addition to the solidbirch bark extract particles. In some embodiments, the oleogel comprisesbetween about 1 wt. % and about 20 wt. % solid birch bark extractdispersed in about 80 wt. % to about 99 wt. % of one or more nonpolarliquids, wherein the oleogel contains at least one oleogel forming agentin addition to the solid birch bark extract particles.

In other embodiments, the oleogel comprises between about 1 wt. % andabout 30 wt. % solid birch bark extract particle dispersed in about 70wt. % to about 99 wt. % of one or more nonpolar liquids, wherein thedispersed solid birch bark extract particles are the only oleogelforming agent in the oleogel. In some embodiments, the oleogel comprisesbetween about 1 wt. % and about 20 wt. % solid birch bark extractdispersed in about 80 wt. % to about 99 wt. % of one or more nonpolarliquids, wherein the oleogel contains at least one oleogel forming agentin addition to the solid birch bark extract particles.

In certain embodiments, the oleogel comprises: about 5 wt. % solid birchbark extract particle dispersed in about 95 wt. % of one or morenonpolar liquids; about 10 wt. % solid birch bark extract particledispersed in about 90 wt. % of one or more nonpolar liquids; about 15wt. % solid birch bark extract particle dispersed in about 85 wt. % ofone or more nonpolar liquids; or about 20 wt. % solid birch bark extractparticle dispersed in about 80 wt. % of one or more nonpolar liquids.

In the foregoing embodiments, the amount of solid birch bark extractparticle (for example, about 1 wt. % and about 20 wt. %) includes up toabout 0.5 wt % of solid birch bark extract particles that are dissolvedin the nonpolar liquid.

Stressing an oleogel by centrifugation provides information on thetendency of the oleogel to separate (or segregate) the nonpolar liquid.In some embodiments of the oleogels of the present disclosure, thesegregation of the nonpolar liquid from the oleogel is less than about10%, about 9%, about 8%, about 7%, about 6%, about 5%, about 4%, about3%, about 2%, about 1%, about 0.5%, or about 0.1% after centrifuging at25° C. for about 30 minutes at 2750 g (e.g., 4,400 rpm).

The oleogels of the present disclosure may be characterized by theirviscosity. In certain embodiments, the viscosity at 200/s of the oleogelranges from about 0.5 to about 4.0 Pa·s and the thixotropy value of theoleogel ranges from about 200 to about 1200 Pa·s as measured accordingto the rotating viscometer method described in Ph. Eur. 2.2.10 using acone-plate viscometer.

The oleogels of the present disclosure may be also characterized bytheir consistency values as determined using a texture analyzer. Textureanalysis is primarily concerned with measurement of the mechanicalproperties of a product calculated from the results of a two cycletexture profile analysis test. Texture analysers perform this test byapplying controlled forces to the product and recording its response inthe form of force, deformation and time.

In present disclosure, consistency is the force [mN] needed to penetrate1 cm into a sample (e.g., oleogel) as measured using a material testingapparatus (Texture analyser) with a cylindrical penetrating object (0.5inch=1.27 cm). The speed of penetration is 0.4 mm/s.

The oleogels of the present disclosure may be distinguished from simplethickened mixtures of the solid birch bark extracts on the basis ofconsistency values. Specifically, the oleogels of the present disclosuremay be characterized by having a consistency value of less than about3000 mN, and at least about 250 mN as measured by a texture analyzer. Insome embodiments, the consistency value of the oleogels is between about300-2000 mN as measured by a texture analyser.

The present disclosure also provides methods for preparing oleogels. Insome embodiments, the method comprises dispersing solid birch barkextract in a suitable nonpolar liquid.

In some embodiments, a sterile wound dressing comprising a pad and atherapeutically effective layer comprising the oleogel of the presentdisclosure is provided. In certain embodiments, the pad is an adsorbentpad. In other embodiments, the pad is any solid material suitable forcovering a wound, including cotton gauze. In some embodiments, thetherapeutically effective layer of oleogel is applied to one or moresurfaces of the pad (e.g., the surface of the pad intended to contactthe skin or wound of the patient directly). In other embodiments, thepad is immersed in the oleogel such that the oleogel is disposed on atleast a portion of the outer surfaces of the pad, and optionally in atleast portions of the interior of the pad.

In some embodiments, the pad can comprise a material suitable fordressing a wound that dissolve when used, releasing the oleogel. Suchmaterials can include absorbable materials comprising collagen,alginate, etc.

The term emulsion relates to heterogeneous systems consisting of twoliquids that are not miscible with each other or only miscible to alimited extent, which are typically designated as phases. In anemulsion, one of the two liquids is dispersed in the other liquid in theform of minute droplets.

In some embodiments, an emulsion comprising the solid birch bark extractof the present disclosure is provided. Other embodiments provideemulsions comprising the oleogels of the present disclosure.

In some embodiments, the emulsions of the present disclosure include anemulsifier. In certain embodiments, the emulsifier is(hydropropyl)methyl cellulose. In certain other embodiments, theemulsions are substantially free of an emulsifier.

For treating skin wounds, foams may be superior to oleogels becausefoams can be applied to wounds almost touchless whereas the applicationof an oleogel requires touch. Foams are generally based on emulsionswhere a propellant is mixed with the dispersed lipid phase of anemulsion.

The present disclosure provides foams comprising a solid birch barkextract-containing emulsion as described above.

In certain embodiments, the foam comprises an oleogel consisting ofabout 5 wt. % to about 10 wt. % solid birch bark extract and theemulsion is a water-in-oil emulsion consisting of the oleogel and about20 wt. % to about 30 wt. % of water.

In certain other embodiments, the foam comprises an oleogel consistingof about 7 wt. % solid birch bark extract and the emulsion is awater-in-oil emulsion consisting of the oleogel and about 25 wt. % ofwater.

In certain embodiments, the foams of the present disclosure furthercomprise an emulsifier. Emulsifiers are well known in the art assubstances that stabilize emulsions, and include surfactants.Emulsifiers useful in the present invention are those that areacceptable for pharmaceutical use, particularly for skin or woundcontact. In some embodiments, suitable emulsifiers include emulsifyingwaxes, cetearyl alcohol, polysorbate 20, ceteareth 20, etc. In certainfurther embodiments, the emulsifier is selected from the groupconsisting of phosphatidyl choline, polyglyceryl-3-methyl glucosedistearate, and combinations thereof.

In certain embodiments, the oleogels, emulsions, and foams of thepresent disclosure further comprise a disinfectant. In certain furtherembodiments, the disinfectant is selected from the group consisting ofethanol, propan-1-ol (n-propanol), and propan-2-ol (isopropanol). Inother embodiments, the oleogels, emulsions, and foams of the presentdisclosure further comprise an antibiotic, particularly lipophilicantibiotics such as fluoroquinolones, macrolides, tigecycline,lincosamides, rifampin, linezolid, tetracyclines, and chloramphenicol.

In certain embodiments, the foams of the present disclosure possesscertain physical properties. In some embodiments, the foam index isgreater than about 2. In other embodiments, the emulsion used in thefoam exhibits an interfacial surface tension of greater than about 4nM/m using methods known in the art. The term “foam index” as usedherein is the ratio of the foamed and unfoamed densities of thespecified material. For example, the foam index of a particular foam isthe ratio of the density of the foamed material to the density of thematerial prior to foaming.

The present disclosure also provides for pressurized containers filledwith an emulsion of the present invention and a pharmaceuticallyacceptable propellant whereby the emulsion forms a foam upon decantingat least a portion of the mixture from the container.

Methods of using Solid Birch Bark Extracts

The present disclosure also provides methods of treating a wound in apatient by topically administering an effective amount of an oleogel, anemulsion or a foam of the present disclosure to at least a portion ofthe wound.

In certain embodiments, the wound treated is selected from the groupconsisting of burns (such as mild to severe burns), surgical skinlesions, superficial injuries, chronic wounds (such as pressure ulcers,diabetic foot ulcers, chronic venous ulcers, artery insufficiencyulcers, etc.), aesthetic skin treatments (such as ablative laser skintreatments, chemical peels, dermabrasion, etc.), wounds resulting fromadverse drug reactions (such as toxic epidermal necrolysis, Lyellsyndrome, Stevens-Johnson syndrome, radiation-induced dermatitis,chemotherapy-induced dermatitis, etc.), rare skin diseases (such asepidermolysis bullosa, pemphigus vulgaris, pemphigoid, bullouspemphigoid, Pemphigus foliaceus, pyoderma gangrinosa, etc.) andcombinations thereof.

The present disclosure also provides methods of treating epidermolysisbullosa in a patient in need thereof comprising topically administeringan effective amount of an oleogel, an emulsion or a foam of the presentdisclosure to an area of epidermolysis bullosa of the patient.

INCORPORATION BY REFERENCE

All references, articles, publications, patents, patent publications,and patent applications cited herein are incorporated by reference intheir entireties for all purposes. However, mention of any reference,article, publication, patent, patent publication, and patent applicationcited herein is not, and should not be taken as acknowledgment or anyform of suggestion that they constitute valid prior art or form part ofthe common general knowledge in any country in the world.

What is claimed is:
 1. A method of treating epidermolysis bullosa in asubject in need thereof, comprising administering to the subject asterile oleogel comprising about 1 wt. % to about 20 wt. % of particlesof a solid birch bark extract having an average particle size of lessthan about 50 μm, dispersed in one or more nonpolar liquids; wherein thesolid birch bark extract comprises at least about 70 wt. % betulin andone or more triterpenes selected from the group consisting of betulinicacid, oleanolic acid, erythrodiol, and lupeol; and wherein the oleogelis sterilized by ionizing irradiation at doses ranging from about 11 toabout 40 kGy.
 2. The method of claim 1, wherein the oleogel issterilized by ionizing irradiation at doses ranging from about 11 toabout 20 kGy.
 3. The method of claim 1, wherein the ionizing radiationis X-ray or gamma radiation.
 4. The method of claim 1, wherein thedispersed solid birch bark extract particles are the only oleogelforming agent in the oleogel.
 5. The method of claim 1, wherein theoleogel comprises about 10 wt. % of particles of the solid birch barkextract.
 6. The method of claim 1, wherein the nonpolar liquid comprisesone or more vegetable oils.
 7. The method of claim 6, wherein thenonpolar liquid is sunflower oil.
 8. The method of claim 1, wherein theoleogel is substantially free of solid birch bark extract particleshaving a size greater than about 50 μm.
 9. The method of claim 1,wherein the segregation of the nonpolar liquid from the oleogel is lessthan about 10% after centrifuging at 25° C. for 30 min at 2750 g. 10.The method of claim 1, wherein the viscosity at 200/s of the oleogelranges from about 0.5 to about 4 Pa·s and the thixotropy value of theoleogel ranges from about 200 to about 1200 Pa·s as measured accordingto the rotating viscometer method described in Ph. Eur. 2.2.10 using acone-plate viscometer.
 11. A method of treating epidermolysis bullosa ina subject in need thereof, comprising administering to the subject anoleogel comprising about 1 wt. % to about 20 wt. % of particles of asolid birch bark extract having an average particle size of less thanabout 50 μm, dispersed in one or more nonpolar liquids; wherein thesolid birch bark extract comprises at least about 70 wt. % betulin andone or more triterpenes selected from the group consisting of betulinicacid, oleanolic acid, erythrodiol, and lupeol; and the oleogel has aconsistency ranging from about 300-3000 mN; wherein the consistency isthe force (mN) needed to penetrate 1 cm into the oleogel as measuredusing a texture analyser with a 1.27 cm cylindrical penetrating object,and the speed of penetration is 0.4 mm/s.
 12. The method of claim 11,wherein the dispersed solid birch bark extract particles are the onlyoleogel forming agent in the oleogel.
 13. The method of claim 11,wherein the oleogel comprises about 10 wt. % of particles of the solidbirch bark extract.
 14. The method of claim 11, wherein the nonpolarliquid comprises one or more vegetable oils.
 15. The method of claim 14,wherein the nonpolar liquid is sunflower oil.
 16. The method of claim11, wherein the oleogel is substantially free of solid birch barkextract particles having a size greater than about 50 μm.
 17. The methodof claim 11, wherein the segregation of the nonpolar liquid from theoleogel is less than about 10% after centrifuging at 25° C. for 30 minat 2750 g.
 18. The method of claim 11, wherein the viscosity at 200/s ofthe oleogel ranges from about 0.5 to about 4 Pa·s and the thixotropyvalue of the oleogel ranges from about 200 to about 1200 Pa·s asmeasured according to the rotating viscometer method described in Ph.Eur. 2.2.10 using a cone-plate viscometer.
 19. A method of treatingepidermolysis bullosa in a subject in need thereof, comprisingadministering the subject an oleogel, prepared by a process comprising:dispersing about 1 wt. % to about 20 wt. % of a dried solid birch barkextract having an average particle size of less than about 50 μm in oneor more non-polar liquids; wherein the solid birch bark extractcomprises at least about 70 wt. % betulin and one or more triterpenesselected from the group consisting of betulinic acid, oleanolic acid,erythrodiol, and lupeol; and wherein the nonpolar liquid has a peroxidevalue less than about
 3. 20. The method of claim 19, wherein the oleogelcomprises about 10 wt. % of particles of the solid birch bark extract.21. The method of claim 19, wherein the nonpolar liquid comprises one ormore vegetable oils.
 22. The method of claim 21, wherein the nonpolarliquid is sunflower oil.
 23. The method of claim 19, wherein the oleogelis substantially free of solid birch bark extract particles having asize greater than about 50 μm.
 24. The method of claim 19, wherein thesegregation of the nonpolar liquid from the oleogel is less than about10% after centrifuging at 25° C. for 30 min at 2750 g.
 25. The method ofclaim 19, wherein the viscosity at 200/s of the oleogel ranges fromabout 0.5 to about 4 Pa·s and the thixotropy value of the oleogel rangesfrom about 200 to about 1200 Pa·s as measured according to the rotatingviscometer method described in Ph. Eur. 2.2.10 using a cone-plateviscometer.
 26. The method of claim 1, comprising topicallyadministering the sterile oleogel to an area of epidermolysis bullosa.27. The method of claim 11, comprising topically administering theoleogel to an area of epidermolysis bullosa.
 28. The method of claim 19,comprising topically administering the oleogel to an area ofepidermolysis bullosa.